WHAT IS DOUBLY REINFORCED BEAMConcrete Have High Compression Strength And Very Low Tensile Strength For In This Reason Steel Reinforcement Is Provided For Tension Zone Because Steel Reinforcement Have High Tensile Strength.For Single Reinforced Beam Reinforcement Is Provided Only Tension Zone Only (Bottom Side Of Beam) Other Case Both Tension And Compression Zone Of Beam Is Provided Reinforcement (Top And Bottom Of Beam ) That Is Called Doubly Reinforced Beam.For Singly Reinforced Beam Minimum Two Numbers Of Bares Provided In Compression zone But It Does Not Consider For Moment Of Resistance Calculation .When We Consider This Reinforced Steel Bas Are Calculation Of Moment Of Resistance At The Time We Have To Provide Additional Tension Steel In Tension Zone Therefore To Reduced The Over Reinforced Section.For Design Of Doubly Reinforced Beam First Find Out Limiting Moment Of Resistance And Area Of Tension Steel ( Ast ) In Singly Reinforced Section Then To Find Area Of Compression Steel (Asc) And Area Of Addition Tension Steel (Ast) To Resistance The Excess Bending Moment (Mu2)

WHEN WE GO FOR DESIGN OF DOUBLY REINFORCED BEAM.The Depth Of Beam May Be Restricted For Some Architecture Reason Or Our Requirement. At That Situation Doubly Reinforced Beam Is designed .If Such Type Of Beam Restricted Depth Are Required To Resist More Moment That Limiting Moment.When Go Design Moment Of Resistance Is Higher Than Limiting Moment Of Resistance. Design Doubly Reinforced Beam.